1. Field of the Invention
The present invention mainly relates to a power amplifier for mobile communications such as cellular phones.
2. Background Art
As a power amplifier for cellular phones such as CDMA, GaAs-HBT power amplifiers are widely used (for example, refer to Patent Document 1: Japanese Patent Laid-Open No. 2004-343244). Conventional power amplifiers have been required to input an exterior reference voltage. Since the reference voltage determines the idle current of the power amplifier, it must be strong to the variation of the power voltage, and must be constantly maintained at high accuracy (for example, approximately 2.85±0.1 V).
In recent years, the generation of reference voltage in the power amplifier has been required. In this case, depending on enable signals (digital signals for turning ON/OFF the power amplifier) supplied from the exterior, a reference voltage is generated in the amplifier, and the power amplifier is operated (for example, refer to Patent Document 2: Japanese Patent Laid-Open No. 2010-124408).